Halogen promoted multi-metal oxide catalyst

ABSTRACT

A catalyst comprising a promoted mixed metal oxide is useful for the vapor phase oxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated carboxylic acid and for the vapor phase ammoxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated nitrile.

This non-provisional application is a divisional of non-provisionalapplication Ser. No. 09/927,941, filed Aug. 10, 2001 and now U.S. Pat.No. 6,461,996, benefit of which is claimed under 35 USC 120, which inturn claims benefit under 35 USC 119(e) of provisional Application No.60/235,977, filed Sep. 28, 2000, priority benefit of which is alsoclaimed for the present application, provisional Application No.60/236,261, filed Sep. 28, 2000, priority benefit of which is alsoclaimed for the present application, provisional Application No.60/236,262, filed Sep. 28, 2000, priority benefit of which is alsoclaimed for the present application, and provisional Application No.60/236,263, filed Sep. 28, 2000, priority benefit of which is alsoclaimed for the present application.

The present invention relates to an improved catalyst for the oxidationof alkanes or a mixture of alkanes and alkenes to their correspondingunsaturated carboxylic acids by vapor phase catalytic oxidation; to amethod of making the catalyst; and to a process for the vapor phasecatalytic oxidation of alkanes or a mixture of alkanes and alkenes totheir corresponding unsaturated carboxylic acids.

The present invention also relates to a method of producing unsaturatednitrites by subjecting alkanes or a mixture of alkanes and alkenes tovapor phase catalytic oxidation in the presence of ammonia.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitrites is to subject an olefin suchas propene or isobutene to a catalytic reaction with ammonia and oxygenin the presence of a catalyst in a gaseous phase at a high temperature.Known catalysts for conducting this reaction include a Mo—B—P—Ocatalyst, a V—Sb—O catalyst, an Sb—U—V—Ni—O catalyst, a Sb—Sn—Ocatalyst, a V—Sb—W—P—O catalyst and a catalyst obtained by mechanicallymixing a V—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view ofthe price difference between propane and propene or between isobutaneand isobutene, attention has been drawn to the development of a methodfor producing acrylonitrile or methacrylonitrile by an ammoxidationreaction wherein a lower alkane, such as propane or isobutane, is usedas a starting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformula

Mo_(a)V_(b)Te_(c)X_(x)O_(n)

wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Similarly, Japanese Laid-Open Patent Application Publication No.6-228073 discloses a method of nitrile preparation comprising reactingan alkane in a gas phase contact reaction with ammonia in the presenceof a mixed metal oxide catalyst of the formula

W_(a)V_(b)Te_(c)X_(x)O_(n)

wherein X represents one or more elements selected from niobium,tantalum, titanium, aluminum, zirconium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony,bismuth, indium and cerium and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0,x=0.01 to 1.0 and n is determined by the oxide form of the elements.

U.S. Pat. No. 6,043,185 also discloses a catalyst useful in themanufacture of acrylonitrile or methacrylonitrile by the catalyticreaction in the vapor phase of a paraffin selected from propane andisobutane with molecular oxygen and ammonia by catalytic contact of thereactants in a reaction zone with a catalyst, wherein the catalyst hasthe empirical formula

Mo_(a)V_(b)Sb_(c)Ga_(d)X_(e)O_(x)

where X is one or more of As, Te, Se, Nb, Ta, W, Ti, Zr, Cr, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, B, In, Ce, Re, Ir, Ge, Sn, Bi, Y, Pr, an alkalimetal and an alkaline earth metal; and when a=1, b=0.0 to 0.99, c=0.01to 0.9, d=0.01 to 0.5, e=0.0 to 1.0 and x is determined by the oxidationstate of the cations present.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but, the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

European Published Patent Application No. 0 630 879 B1 discloses aprocess for producing an unsaturated aldehyde and a carboxylic acidwhich comprises subjecting propene, isobutene or tertiary butanol to gasphase catalytic oxidation with molecular oxygen in the presence of (i) acatalyst composite oxide represented by the formula

Mo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)

wherein A represents Ni and/or Co, B represents at least one elementselected from Mn, Zn, Ca, Mg, Sn and Pb, C represents at least oneelement selected from P, B, As, Te, W, Sb and Si, and D represents atleast one element selected from K, Rb, Cs and Tl; and wherein, whena=12, 0<b≦10, 0<c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦20 and 0≦g≦2, and x has avalue dependent on the oxidation state of the other elements; and (ii) amolybdenum oxide which in itself is substantially inert to said gasphase catalytic oxidation to provide the corresponding unsaturatedaldehyde and unsaturated carboxylic acid.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Published International Application No. WO 00/09260 discloses a catalystfor selective oxidation of propene to acrylic acid and acroleincontaining a catalyst composition comprising the elements Mo, V, La, Pd,Nb and X in the following ratio:

Mo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(f)

wherein X is Cu or Cr or a mixture thereof,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2

d is 0.0000001 to 0.2,

e is 0 to 0.2, and

f is 0 to 0.2; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, La, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:

0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Published International Application No. WO 00/29106 discloses a catalystfor selective oxidation of propane to oxygenated products includingacrylic acid, acrolein and acetic acid, said catalyst system containinga catalyst composition comprising

Mo_(a)V_(b)Ga_(c)Pd_(d)Nb_(e)X_(f)

wherein X is at least one element selected from La, Te, Ge, Zn, Si, Inand W,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2,

d is 0.0000001 to 0.2,

e is >0 to 0.2, and

f is 0.0 to 0.5; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, Ga, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Japanese Laid-Open Patent Application Publication No. 2000-037623discloses a method for producing an unsaturated carboxylic acidcomprising subjecting an alkane to a vapor phase catalytic oxidation inthe presence of a catalyst having the empirical formula

MoV_(a)Nb_(b)X_(c)Z_(d)O_(n)

wherein X is at least one element selected from the group consisting ofTe and Sb, Z is at least one element selected from the group consistingof W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B,Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earthelements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determinedby the oxidation states of the other elements.

Despite the above-noted attempts to provide new and improved catalystsfor the oxidation of alkanes to unsaturated carboxylic acids and for theammoxidation of alkanes to unsaturated nitriles, one impediment to theprovision of a commercially viable process for such catalytic oxidationsis the identification of a catalyst providing adequate conversion andsuitable selectivity, thereby providing sufficient yield of theunsaturated product.

By the present invention, there are provided promoted catalysts whereinthe activity and selectivity are greatly enhanced as to the basecatalyst and, hence, the overall yield of the desired reaction productis also greatly enhanced.

Thus, in a first aspect, the present invention provides a catalystcomprising a promoted mixed metal oxide having the empirical formula

A_(a)M_(b)N_(c)X_(d)Z_(e)O_(f)

wherein A is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, X is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is anelement selected from the group consisting of Br, Cl, F and I; andwherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001to 0.1 and f is dependent on the oxidation state of the other elements.

In a second aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing apromoted mixed metal oxide having the empirical formula

A_(a)M_(b)N_(c)X_(d)Z_(e)O_(f)

wherein A is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, X is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is anelement selected from the group consisting of Br, Cl, F and I; andwherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001to 0.1 and f is dependent on the oxidation state of the other elements.

In a third aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing apromoted mixed metal oxide having the empirical formula

A_(a)M_(b)N_(c)X_(d)Z_(e)O_(f)

wherein A is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, X is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is anelement selected from the group consisting of Br, Cl, F and I; andwherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001to 0.1 and f is dependent on the oxidation state of the other elements.

In a fourth aspect, the present invention provides a catalyst producedby the process comprising:

(1) admixing compounds of the elements A, M, N, X and Z and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and Z is an element selected from the group consisting ofBr, Cl, F and I, and wherein the elements A, M, N, X and Z are presentin such amounts that the atomic ratio of A:M:N:X:Z is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to 0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

In a fifth aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N, X and Z and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and Z is an element selected from the group consisting ofBr, Cl, F and I, and wherein the elements A, M, N, X and Z are presentin such amounts that the atomic ratio of A:M:N:X:Z is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to 0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

In a sixth aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N, X and Z and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and Z is an element selected from the group consisting ofBr, Cl, F and I, and wherein the elements A, M, N, X and Z are presentin such amounts that the atomic ratio of A:M:N:X:Z is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to 0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

In a seventh aspect, the present invention provides a catalyst producedby the process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor in the presence of a source ofhalogen, wherein said halogen is Br, Cl, F or I.

In an eighth aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor in the presence of a source ofhalogen, wherein said halogen is Br, Cl, F or I.

In a ninth aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor in the presence of a source ofhalogen, wherein said halogen is Br, Cl, F or I.

In a tenth aspect, the present invention provides a catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor;

(3) calcining said catalyst precursor;

(4) contacting said calcined catalyst precursor with a source ofhalogen, wherein said halogen is Br, Cl, F or I.

In an eleventh aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor;

(3) calcining said catalyst precursor;

(4) contacting said calcined catalyst precursor with a source ofhaolgen, wherein said halogen is Br, Cl, F or I.

In a twelfth aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atlest one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is

1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to 0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor;

(3) calcining said catalyst precursor; and

(4) contacting said calcined catalyst precursor with a source ofhalogen, wherein said halogen is Br, Cl, F or I.

The promoted mixed metal oxide to be used as a catalyst component of thepresent invention may have the empirical formula

A_(a)M_(b)N_(c)X_(d)Z_(e)O_(f)

wherein A is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, X is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is anelement selected from the group consisting of Br, Cl, F and I; andwherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001to 0.1 and f is dependent on the oxidation state of the other elements.

Preferably, when a=1, b=0.1 to 0.5, c=0.05 to 0.5, d=0.01 to 0.5 ande=0.002 to 0.1. More preferably, when a=1, b=0.15 to 0.45, c=0.05 to0.45, d=0.01 to 0.1 and e=0.002 to 0.04. The value of f, i.e. the amountof oxygen present, is dependent on the oxidation state of the otherelements in the catalyst. However, f is typically in the range of from 3to 4.7.

Preferred promoted mixed metal oxides have the empirical formulaeMo_(a)V_(b)Te_(c)Nb_(d)Z_(e)O_(f) and W_(a)V_(b)Te_(c)Nb_(d)Z_(e)O_(f)wherein Z, a, b, c, d, e and f are as previously defined.

Further, as the promoted mixed metal oxide, one having a certainspecific crystal structure is preferred. Specifically, preference isgiven to the one which exhibits the following five main diffractionpeaks at specific diffraction angles 2θ in the X-ray diffraction patternof the promoted mixed metal oxide (as measured using Cu—Kα radiation asthe source):

X-ray lattice plane Diffraction angle 2θ Spacing medium Relative (±0.3°)(Å) intensity 22.1° 4.02 100 28.2° 3.16 20˜450 36.2° 2.48 5˜60 45.2°2.00 2˜40 50.0° 1.82 2˜40

The intensity of the X-ray diffraction peaks may vary upon the measuringof each crystal. However, the intensity, relative to the peak intensityat 22.1° being 100, is usually within the above ranges. Generally, thepeak intensities at 2θ=22.1° and 28.2° are distinctly observed. However,so long as the above five diffraction peaks are observable, the basiccrystal structure is the same even if other peaks are observed inaddition to the five diffraction peaks, and such a structure is usefulfor the present invention.

The promoted mixed metal oxide can be prepared in the following manner.

In a first step a slurry or solution may be formed by admixing metalcompounds, preferably at least one of which contains oxygen, and atleast one solvent in appropriate amounts to form the slurry or solution.Preferably, a solution is formed at this stage of the catalystpreparation. Generally, the metal compounds contain elements A, M, N, X,Z and O, as previously defined.

Suitable solvents include water; alcohols including, but not limited to,methanol, ethanol, propanol, and diols, etc.; as well as other polarsolvents known in the art. Generally, water is preferred. The water isany water suitable for use in chemical syntheses including, withoutlimitation, distilled water and de-ionized water. The amount of waterpresent is preferably an amount sufficient to keep the elementssubstantially in solution long enough to avoid or minimize compositionaland/or phase segregation during the preparation steps. Accordingly, theamount of water will vary according to the amounts and solubilities ofthe materials combined. However, as stated above, the amount of water ispreferably sufficient to ensure an aqueous solution is formed, and not aslurry, at the time of mixing.

For example, when a mixed metal oxide of the formulaMo_(a)V_(b)Te_(c)Nb_(d)Br_(e)O_(f) wherein the element A is Mo, theelement M is V, the element N is Te, the element X is Nb and the elementZ is Br, is to be prepared, an aqueous solution of niobium oxalate and asolution of bromine in aqueous nitric acid may be added to an aqueoussolution or slurry of ammonium heptamolybdate, ammonium metavanadate andtelluric acid, so that the atomic ratio of the respective metal elementswould be in the prescribed proportions.

Once the aqueous slurry or solution (preferably a solution) is formed,the water is removed by any suitable method, known in the art, to form acatalyst precursor. Such methods include, without limitation, vacuumdrying, freeze drying, spray drying, rotary evaporation and air drying.Vacuum drying is generally performed at pressures ranging from 10 mmHgto 500 mmHg. Freeze drying typically entails freezing the slurry orsolution, using, for instance, liquid nitrogen, and drying the frozenslurry or solution under vacuum. Spray drying is generally performedunder an inert atmosphere such as nitrogen or argon, with an inlettemperature ranging from 125° C. to 200° C. and an outlet temperatureranging from 75° C. to 150° C. Rotary evaporation is generally performedat a bath temperature of from 25° C. to 90° C. and at a pressure of from10 mmHg to 760 mmHg, preferably at a bath temperature of from 40° to 90°C. and at a pressure of from 10 mmHg to 350 mmHg, more preferably at abath temperature of from 40° C. to 60° C. and at a pressure of from 10mmHg to 40 mmHg. Air drying may be effected at temperatures ranging from25° C. to 90° C. Rotary evaporation or air drying are generallypreferred.

Once obtained, the catalyst precursor is calcined. The calcination maybe conducted in an oxygen-containing atmosphere or in the substantialabsence of oxygen, e.g., in an inert atmosphere or in vacuo. The inertatmosphere may be any material which is substantially inert, i.e., doesnot react or interact with, the catalyst precursor. Suitable examplesinclude, without limitation, nitrogen, argon, xenon, helium or mixturesthereof. Preferably, the inert atmosphere is argon or nitrogen. Theinert atmosphere may flow over the surface of the catalyst precursor ormay not flow thereover (a static environment). When the inert atmospheredoes flow over the surface of the catalyst precursor, the flow rate canvary over a wide range, e.g., at a space velocity of from 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, the catalyst precursor is calcined intwo stages. In the first stage, the catalyst precursor is calcined in anoxidizing environment (e.g. air) at a temperature of from 200° C. to400° C., preferably from 275° C. to 325° C. for from 15 minutes to 8hours, preferably for from 1 to 3 hours. In the second stage, thematerial from the first stage is calcined in a non-oxidizing environment(e.g., an inert atmosphere) at a temperature of from 500° C. to 750° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, the catalyst precursor inthe first stage is placed in the desired oxidizing atmosphere at roomtemperature and then raised to the first stage calcination temperatureand held there for the desired first stage calcination time. Theatmosphere is then replaced with the desired non-oxidizing atmospherefor the second stage calcination, the temperature is raised to thedesired second stage calcination temperature and held there for thedesired second stage calcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

With calcination, a catalyst is formed having the formulaA_(a)M_(b)N_(c)X_(d)Z_(e)O_(f) wherein A, M, N, X, Z, O, a, b, c, d, eand f are as previously defined.

The starting materials for the above promoted mixed metal oxide are notlimited to those described above. A wide range of materials including,for example, oxides, nitrates, halides or oxyhalides, alkoxides,acetylacetonates, and organometallic compounds may be used.

For example, ammonium heptamolybdate may be utilized for the source ofmolybdenum in the catalyst. However, compounds such as MoO₃, MoO₂,MoCl₅, MoOCl₄, Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdicacid and silicomolybdic acid may also be utilized instead of ammoniumheptamolybdate.

Similarly, ammonium metavanadate may be utilized for the source ofvanadium in the catalyst. However, compounds such as V₂O₅, V₂O₃, VOCl₃,VCl₄, VO(OC₂H₅)₃, vanadium acetylacetonate and vanadyl acetylacetonatemay also be utilized instead of ammonium metavanadate.

The tellurium source may include telluric acid, TeCl₄, Te(OC₂H₅)₅,Te(OCH(CH₃)₂)₄ and TeO₂. The niobium source may include ammonium niobiumoxalate, Nb₂O₅, NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the moreconventional niobium oxalate.

The bromine source may be added as one of the above reagents as abromide or as the bromide salt of X (where X is at least one elementselected from the group consisting of Nb. Ta, Ti, Al, Zr, Cr, Mn, Fe,Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb andLu), for example, as molybdenum bromide, tellurium tetrabromide, niobiumbromide or vanadium bromide; or as a solution of bromine in an aqueousinorganic acid, e.g., nitric acid, during the catalyst precursorpreparation steps. The bromine source may also be added during thecalcination of the catalyst precursor or, after calcination, as abromine treatment step. For example, the bromine source may be added tothe calcination atmosphere or to the oxidation reactor feed stream, as,for example, HBr, Br₂, ethyl bromide or the like, to achieve apromotional effect with the bromine. The bromine source is preferablyadded in an amount so as to provide an atomic ratio of Br: element(s) Aof 0.001 to 1:1 in the final catalyst composition.

The chlorine source may be added as one of the above reagents as achloride or as the chloride salt of X (where X is at least one elementselected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe,Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb andLu), for example, as molybdenum chloride, tellurium tetrachloride,niobium chloride or vanadium chloride, during the catalyst precursorpreparation steps. The chlorine source may also be added during thecalcination of the catalyst precursor or, after calcination, as achlorine treatment step. For example, the chlorine source may be addedto the calcination atmosphere or to the oxidation reactor feed stream,as, for example, HCl, Cl₂, ethyl chloride or the like, to achieve apromotional effect with the chloride. The chlorine source is preferablyadded added in an amount so as to provide an atomic ratio of Cl:element(s) A of 0.001 to 0.1:1 in the final catalyst composition.

The fluorine source may be added as one of the above reagents as afluoride or as the fluoride salt of X (where X is at least one elementselected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe,Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb andLu), for example, as molybdenum fluoride, tellurium fluoride, niobiumfluoride or vanadium fluoride, during the catalyst precursor preparationsteps. The fluorine source may also be added during the calcination ofthe catalyst precursor or, after calcination, as a fluorine treatmentstep. For example, the fluorine source may be added to the calcinationatmosphere or to the oxidation reactor feed stream, as, for example, HF,F₂, ethyl fluoride or the like, to achieve a promotional effect with thefluoride. The fluorine source is preferably added in an amount so as toprovide an atomic ratio of

F: element(s) A of 0.001 to 0.1:1 in the final catalyst composition.

The iodine source may be added as one of the above reagents as afluoride or as the fluoride salt of X (where X is at least one elementselected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe,Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb andLu), for example, as molybdenum iodide, tellurium iodide, niobium iodideor vanadium iodide, during the catalyst precursor preparation steps. Theiodine source may also be added during the calcination of the catalystprecursor or, after calcination, as an iodine treatment step. Forexample, the iodine source may be added to the calcination atmosphere orto the oxidation reactor feed stream, as, for example, HI, I₂, ethyliodide or the like, to achieve a promotional effect with the iodide. Theiodine source is preferably added in an amount so as to provide anatomic ratio of

I: element(s) A of 0.001 to 0.1:1 in the final catalyst composition.

A promoted mixed metal oxide, thus obtained, exhibits excellentcatalytic activities by itself. However, the promoted mixed metal oxidecan be converted to a catalyst having higher activities by grinding.

There is no particular restriction as to the grinding method, andconventional methods may be employed. As a dry grinding method, a methodof using a gas stream grinder may, for example, be mentioned whereincoarse particles are permitted to collide with one another in a highspeed gas stream for grinding. The grinding may be conducted not onlymechanically but also by using a mortar or the like in the case of asmall scale operation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus. However, it ispreferred that grinding is conducted until the average particle size ofthe ground catalyst precursor would usually be at most 20 μm, morepreferably at most 5 μm. Improvement in the catalytic performance mayoccur due to such grinding.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The oxide obtained by the above-mentioned method may be used as a finalcatalyst, but it may further be subjected to heat treatment usually at atemperature of from 200° to 700° C. for from 0.1 to 10 hours.

The promoted mixed metal oxide thus obtained may be used by itself as asolid catalyst, but may be formed into a catalyst together with asuitable carrier such as silica, alumina, titania, aluminosilicate,diatomaceous earth or zirconia. Further, it may be molded into asuitable shape and particle size depending upon the scale or system ofthe reactor.

Alternatively, the metal components of the presently contemplatedcatalyst may be supported on materials such as alumina, silica,silica-alumina, zirconia, titania, etc. by conventional incipientwetness techniques. In one typical method, solutions containing themetals are contacted with the dry support such that the support iswetted; then, the resultant wetted material is dried, for example, at atemperature from room temperature to 200° C. followed by calcinationand/or post-treatment as described above. In another method, metalsolutions are contacted with the support, typically in volume ratios ofgreater than 31 (metal solution: support), and the solution agitatedsuch that the metal ions are ion-exchanged onto the support. Themetal-containing support is then dried and calcined and/or post-treatedas detailed above.

In further aspects, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane, or a mixture of an alkane and an alkene, to a vapor phasecatalytic oxidation reaction in the presence of a catalyst according tothe present invention, to produce an unsaturated carboxylic acid.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas which contains steam. Insuch a case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas):(H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20):(0.2 to 70), more preferably (1):(1to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is preferred to employ a mixture of C₃₋₈alkane andC₃₋₈alkene, particularly propane and propene, isobutane and isobutene orn-butane and n-butene. As the starting material mixture of alkane andalkene, propane and propene or isobutane and isobutene are morepreferred. Most preferred is a mixture of propane and propene. Accordingto the present invention, from such a mixture of an alkane and analkene, an unsaturated carboxylic acid such as an α,β-unsaturatedcarboxylic acid can be obtained in good yield. For example, when propaneand propene or isobutane and isobutene are used as the starting materialmixture of alkane and alkene, acrylic acid or methacrylic acid will beobtained, respectively, in good yield. Preferably, in the mixture ofalkane and alkene, the alkene is present in an amount of at least 0.5%by weight, more preferably at least 1.0% by weight to 95% by weight;most preferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above promoted mixed metaloxide or by molecular oxygen present in the feed gas. To incorporatemolecular oxygen into the feed gas, such molecular oxygen may be pureoxygen gas. However, it is usually more economical to use anoxygen-containing gas such as air, since purity is not particularlyrequired.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

These further aspects of the present invention will be described infurther detail with respect to a case where propane is used as thestarting material alkane and air is used as the oxygen source. Thereaction system may be a fixed bed system or a fluidized bed system.However, since the reaction is an exothermic reaction, a fluidized bedsystem may preferably be employed whereby it is easy to control thereaction temperature. The proportion of air to be supplied to thereaction system is important for the selectivity for the resultingacrylic acid, and it is usually at most 25 moles, preferably from 0.2 to18 moles per mole of propane, whereby high selectivity for acrylic acidcan be obtained. This reaction can be conducted usually underatmospheric pressure, but may be conducted under a slightly elevatedpressure or slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reaction is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problemwhich enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. In such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

In still further aspects, the present invention provides processes forsubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction with ammonia in the presence ofa catalyst containing the above mixed metal oxide, to produce anunsaturated nitrile.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈alkane such as propane,butane, isobutane, pentane, hexane and heptane. However, in view of theindustrial application of nitriles to be produced, it is preferred toemploy a lower alkane having 3 or 4 carbon atoms, particularly propaneand isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispreferred to employ a mixture of C₃₋₈alkane and C₃₋₈alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitriles to be produced, it ismore preferred to employ a mixture of a lower alkane having 3 or 4carbon atoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

These still further aspects of the present invention will be describedin further detail with respect to a case where propane is used as thestarting material alkane and air is used as the oxygen source. Theproportion of air to be supplied for the reaction is important withrespect to the selectivity for the resulting acrylonitrile. Namely, highselectivity for acrylonitrile is obtained when air is supplied within arange of at most 25 moles, particularly 1 to 15 moles, per mole of thepropane. The proportion of ammonia to be supplied for the reaction ispreferably within a range of from 0.2 to 5 moles, particularly from 0.5to 3 moles, per mole of propane. This reaction may usually be conductedunder atmospheric pressure, but may be conducted under a slightlyincreased pressure or a slightly reduced pressure. With respect to otheralkanes such as isobutane, or to mixtures of alkanes and alkenes such aspropane and propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The processes of these still further aspects of the present inventionmay be conducted at a temperature of, for example, from 250° C. to 480°C. More preferably, the temperature is from 300° C. to 400° C. The gasspace velocity, SV, in the gas phase reaction is usually within therange of from 100 to 10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹,more preferably from 300 to 2,000 hr⁻¹. As a diluent gas, for adjustingthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium can be employed. When ammoxidation of propaneis conducted by the method of the present invention, in addition toacrylonitrile, carbon monoxide, carbon dioxide, acetonitrile,hydrocyanic acid and acrolein may form as by-products.

EXAMPLES

Catalyst Preparation

Comparative Example 1

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23 Te), formed by dissolving the corresponding salts in water at 70°C., was added to a 1000 mL rotavap flask. Then 50 mL of an aqueoussolution of niobium oxalate (0.25M Nb) and oxalic acid (0.31M) wereadded thereto. After removing the water via a rotary evaporator with awarm water bath at 50° C. and 28 mm/Hg, the solid materials were furtherdried in a vacuum oven at 25° C. overnight and then calcined.(Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours.) The final catalyst had a nominalcomposition of Mo₁V_(0.3)Te_(0.23) Nb_(0.125)O_(f). The catalyst, thusobtained, was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 1

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23 Te), formed by dissolving the corresponding salts in water at 70°C., was added to a 1000 mL rotavap flask. Then 50 mL of an aqueoussolution of niobium oxalate (0.25M Nb) and oxalic acid (0.31M) and 10 mLof an aqueous solution of MoBr₃ (0.033M) were added thereto. Afterremoving the water via a rotary evaporator with a warm water bath at 50°C. and 28 mm/Hg, the solid materials were further dried in a vacuum ovenat 25° C. overnight. 34 grams of solid catalyst precursor wererecovered. 17 grams of this solid precursor were calcined by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition ofBr_(0.01)Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). The catalyst, thusobtained, was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 2

50 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23 Te), formed by dissolving the corresponding salts in water at 70°C., was added to a 1000 mL rotavap flask. Then 25 mL of an aqueoussolution of niobium oxalate (0.25M Nb) and oxalic acid (0.31M) and 10 mLof an aqueous solution of MoCl₅ (0.02M) were added thereto. Afterremoving the water via a rotary evaporator with a warm water bath at 50°C. and 28 mm/Hg, the solid materials were further dried in a vacuum ovenat 25° C. overnight. This solid precursor were calcined by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition ofCl_(0.02)Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). The catalyst, thusobtained, was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Comparative Example 2

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23 Te), formed by dissolving the corresponding salts in water at 70°C., was added to a 1000 mL rotavap flask. Then 50 mL of an aqueoussolution of niobium oxalate (0.16M Nb) and oxalic acid (0.58M) wereadded thereto. After removing the water via a rotary evaporator with awarm water bath at 50° C. and 28 mm/Hg, the solid materials were furtherdried in a vacuum oven at 25° C. overnight and then calcined.(Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours.) The final catalyst had a nominalcomposition of Mo₁V_(0.3)Te_(0.23) Nb_(0.08)O_(f). The catalyst, thusobtained, was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 3

7 grams of the catalyst from Example 1 were ground into powder and thenimpregnated with 3.5 mL of 0.033M VF₃ in H₂O. After removing the watervia a rotary evaporator with a warm water bath at 50° C. and 28 mm/Hg,the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. (Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours.) The final catalysthad a nominal composition of F_(0.01)Mo₁V_(0.33)Te_(0.23)Nb_(0.08)O_(f).The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Example 4

7 grams of the catalyst from Example 1 were ground into powder and thenimpregnated with 3.5 mL of 0.033M VI₃ in H₂O. After removing the watervia a rotary evaporator with a warm water bath at 50° C. and 28 mm/Hg,the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. (Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours.) The final catalysthad a nominal composition of I_(0.01)Mo₁V_(0.33)Te_(0.23)Nb_(0.08)O_(f). The catalyst, thus obtained, was pressed in a mold andthen broken and sieved to 10-20 mesh granules for reactor evaluation.

Evaluation and Results

Catalysts were evaluated in a 10 cm long Pyrex tube reactor (internaldiameter: 3.9 mm). The catalyst bed (4 cm long) was positioned withglass wool at approximately mid-length in the reactor and was heatedwith an electric furnace. Mass flow controllers and meters regulated thegas flow rate. The oxidation was conducted using a feed gas stream ofpropane, steam and air, with a feed ratio of propane:steam:air of1:3:96. The reactor effluent was analyzed by an FTIR. The results at390° C. and at a 3 second residence time are shown in Table 1.

TABLE 1 Example % C3 Conv. % AA Yield % AA Sel. Comp. Ex 1 41 17 41 Ex.1 44 25 57 Ex. 2 54 30 55 Comp. Ex. 2 71 13 18 Ex. 3 61 31 51 Ex. 4 5129 58

What is claimed is:
 1. A process for producing an unsaturated carboxylicacid, which comprises subjecting an alkane or a mixture of an alkane andan alkene to a vapor phase catalytic oxidation reaction in the presenceof a catalyst containing a promoted mixed metal oxide having theempirical formula A_(a)M_(b)N_(c)X_(d)Z_(e)O_(f) wherein A is at leastone element selected from the group consisting of Mo and W, M is atleast one element selected from the group consisting of V and Ce, N isat least one element selected from the group consisting of Te, Sb andSe, X is at least one element selected from the group consisting of Nb,Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge,Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu,Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is an element selected fom thegroup consisting of Br, Cl, F and I; and wherein, when a=1, b=0.01 to1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001 to 0.1 and f is dependent onthe oxidation state of the other elements.
 2. A process for producing anunsaturated carboxylic acid, which comprises subjecting an alkane or amixture of an alkane and an alkene to a vapor phase catalytic oxidationreaction in the presence of a catalyst produced by the processcomprising: (1) admixing compounds of the elements A, M, N, X and Z andat least on solvent to form an admixture, wherein A is at least oneelement selected from the group consisting of Mo and W, M is at leastone element selected from the group consisting of V and Ce, N is atleast one element selected from the the group consisting of Te, Sb andSe, X is at least one element selected from the group consisting of Nb,Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn,Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd,Dy, Ho, Er, Tm, Yb and Lu, and Z is an element selectd from the groupconsisting of Br, Cl, F and I, and wherein the elements A, M, N, X and Zare present in such amounts that the atomic ratio of A:M:N:X:Z is 1:0.01to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to 0.1; (2) removing said at leastone solvent from the admixture to obtain a catalyst precursor; and (3)calcining said catalyst precursor.
 3. A process for producing anunsaturated carboxylic acid, which comprises subjecting an alkane or amixture of an alkane and an alkene to a vapor phase catalytic oxidationreaction in the presence of a catalyst produced by the processcomprising: (1) admixing compounds of the elements A, M, N and X and atleast one solvent to form an admixture, wherein A is at least oneelement selected from the group consisting of Mo and W, M is at leastone elemnt selected from the group consisting of V and Ce, N is at leastone element selected from the group consisting of Te, Sb and Se, and Xis at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li,Na, K, Rb, Cs, r, e, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho,Er, Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is 1:0.01 to 1.0:0.01 to1.0:0.01 to 1.0; (2) removing said at least one solvent from theadmixture to obtain a catalyst precursor; and (3) calcining saidcatalyst precursor in the presence of a source of halogen, wherein saidhalogen is Br, Cl, F or I.
 4. A process for producing an unsaturatedcarboxylic acid, which comprises subjecting an alkane or a mixture of analkane and an alkene to a vapor phase catalytic oxidation reaction inthe presence of a catalyst produced by the process comprising: (1)admixing compounds of the elements A, M, N and X and at least onesolvent to form an admixture, wherein A is at least one element selectedfrom the group consisting of Mo and W, M is at least one elementselected from the group consisting of V and Ce, N is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, and wherein the elements A, M, N and X are present insuch amounts that the atomic ratio of A:M:N:X is 1:0.01 to 1.0:0.01 to1.0:0.01 to 1.0; (2) removing said at least one solvnt from theadmixture to obtain catalyst precursor; (3) calcining said catalystprecursor; and (4) contacting said calcined catalyst precursor with asource of halogen, wherein said halogen is Br, Cl, F or I.